Synthetic muscle that lifts
1,000 TIMES its own weight could lead to super-strong
humanoid robots

The artificial muscle can push, pull, bend and twist, as well
as lift heavy weightsIt does so at low voltage without the need for an external
compressor systemIt is actuated using a thin resistive wire and an eight volt
low-power supplyIt is 3D printed into a silicone rubber matrix with ethanol
distributed throughout

By Tim Collins

Humanoid robots are a step closer after engineers developed
synthetic muscle that can lift a thousand times its own weight.

The artificial muscle can push, pull, bend and twist, as well as
lift weight.

A team of engineers at Columbia University says up until now no
material has been capable of functioning as a soft muscle.

This is due to an inability to show the desired properties of high
stress and strain.

Inspired by living organisms, team leader Professor Hod Lipson
said soft material robotics hold 'great promise' for areas where
robots need to contact and interact with humans, such as
manufacturing and healthcare.

He said that, unlike rigid robots, soft robots can replicate
natural motion, grasping and manipulation, to provide medical and
other types of assistance, perform delicate tasks, or pick up soft
objects.

Professor Lipson added: 'We've been making great strides toward
making robot minds, but robot bodies are still primitive.

'This is a big piece of the puzzle and, like biology, the new
actuator can be shaped and reshaped a thousand ways.

'We've overcome one of the final barriers to making lifelike
robots.'

To achieve an actuator with high strain and high stress coupled
with low density, study lead author Aslan Miriyev used a silicone
rubber matrix with ethanol distributed throughout in
micro-bubbles.

HOW IT WAS DONE

To achieve an actuator with high strain and high stress coupled
with low density, study lead author Aslan Miriyev used a silicone
rubber matrix with ethanol distributed throughout in
micro-bubbles.

The solution combined the elastic properties and extreme volume
change attributes of other material systems, while also being easy
to fabricate, low cost, and made of environmentally safe
materials.

After being 3D-printed into the desired shape, the artificial
muscle was electrically actuated using a thin resistive wire and
eight volt low-power.

It was tested in a range of robotic applications where it showed
significant expansion-contraction ability.

It was capable of expansion up to 900 per cent when electrically
heated to 80°C (176°F).

Via computer controls, the autonomous unit is capable of
performing motion tasks in almost any design.

A self-contained soft actuator three times stronger than natural
muscle, without the need of externals, signals a breakthrough in
soft robotics. The artificial muscle in use as a bicep lifts a
skeleton’s arm to a 90 degree position. Researchers at Columbia
Engineering have solved a long-standing issue in the creation of
untethered soft robots whose actions and movements can help mimic
natural biological systems. Aslan Miriyev and Kenneth Stack, in
the Creative Machines lab led by Hod Lipson, professor of
mechanical engineering, have developed a 3D-printable synthetic
soft muscle, a one-of-a-kind artificial active tissue with
intrinsic expansion ability that does not require an external
compressor or high voltage equipment as previous muscles required.

Inspired by natural muscle, a key challenge in soft robotics is to
develop self-contained electrically driven soft actuators with
high strain density. Various characteristics of existing
technologies, such as the high voltages required to trigger
electroactive polymers ( > 1KV), low strain ( < 10%) of
shape memory alloys and the need for external compressors and
pressure-regulating components for hydraulic or pneumatic
fluidicelastomer actuators, limit their practicality for
untethered applications. Here we show a single self-contained soft
robust composite material that combines the elastic properties of
a polymeric matrix and the extreme volume change accompanying
liquid–vapor transition. The material combines a high strain (up
to 900%) and correspondingly high stress (up to 1.3 MPa) with low
density (0.84 g cm−3). Along with its extremely low cost (about 3
cent per gram), simplicity of fabrication and
environment-friendliness, these properties could enable new kinds
of electrically driven entirely soft robots.

Introduction

Inspired by biology, researchers aim to develop soft-bodied
programmable motion in order to combine natural compliance with
controllable actuation. One of the long standing challenges has
been the lack of easily processed robust soft actuators with high
strain density 1,2,3,4,5. Such actuators would be easy to produce
and to mold, cut, and 3D print into a desired shape, yet would
produce large macroscopic actuation at relatively low voltage and
current. Today, soft actuation techniques are based on either
electroactive polymers 6,7,8,9,10,11,12, shape memory alloys and
shape memory polymers13,14,15, or compressed air and pressurized
fluids actuators 16,17,18,19,20,21,22,23,24. However, the high
voltages required to trigger electroactive polymers ( > 1KV)
and low strain ( < 10%) of shape memory alloys, as well as the
need for external compressors and pressure-regulating components
for hydraulic16, 18, 21, 24 or pneumatic 16, 17, 19, 20, 22, 23
fluidic elastomer actuators, limit their miniaturization2, 4, 16
and practicality for untethered applications. Recent
demonstrations of actuation based on combustion25 are ideal for
impact delivery, but are less suitable for controllable
kinematics.

Phase change materials offer an attractive alternative to
conventional electromechanical actuators. Such materials rely on
the mechanical force produced by the rapid expansion that occurs
at the phase transition temperature. One of the classic examples
of phase change materials is paraffin, which thermomechanical
properties were first utilized in early 1930s26 for
self-regulating vents in greenhouses.While paraffin-based
actuators can deliver large forces, their strain remains in the
order of 10% volumetric change26,27,28, a strain that is on par
with shape memory alloys and too small for most robotics
applications.

A significantly higher expansion strain may be achieved by
utilizing reversible liquid–vapor phase transition, but such
material systems have been traditionally difficult to contain and
control. A number of recent devices use entrapped liquid inside
balloons or between thin films, to form expanding
cavities29,30,31,32. Electrically triggered deformation of soft
elastomer membranes, utilizing liquid–gas transition of liquid,
was reported to show large area expansion33. However, such devices
are challenging to manufacture and to form into arbitrary shapes
because of their intricate internal design. For example, it is
difficult to directly cast or 3D-print any of these actuators.

Here we propose a single easily prepared soft robust material that
combines the elastic properties of a polymeric matrix and the
extreme volume change of a fluid upon liquid–vapor transition. We
show and characterize the soft composite material comprised of a
silicone elastomer matrix with ethanol distributed throughout it
in micro-bubbles, exhibiting strains up to 900%, and demonstrate
its use as an actuator in a range of robotic applications.

ResultsMaterials system and its principles of action

Choosing a polymer matrix and a fluid for the composite
meta-material system was guided by the desired mechanical
properties of a polymer, boiling point and practical handling
restrictions of a fluid, and chemical compatibility of the two. We
aimed to synthesize a cheap, simple, user- and
environment-friendly material comprised of food-safe and
bio-compatible materials. We chose PDMS-based silicone elastomer,
a non-hazardous elastomer widely used for soft robotic
applications, as a matrix material, and ethanol, a widely used
alcohol with boiling temperature 78.4 °C and matrix-compatibility,
as the active fluid (Supplementary Fig. 1 and Supplementary
Discussion for a discussion of the material components choice).

Ethanol, included inside tiny micro-bubbles embedded in the
elastic silicone rubber matrix, boils upon reaching the liquid–gas
transition temperature, accompanied by tremendous increase in
volume, leading to significant expansion of the whole soft
composite material. This composite material may be quickly and
easily prepared by mixing ethanol with silicone elastomer
(Supplementary Movie 1, Supplementary Software 1). The mixed
material is both castable and 3D-printable (Supplementary Movies
2, 4), and after preparation will solidify in room-temperature
curing. We successfully mixed various amounts of ethanol
(0–33 vol%) in the two-part platinum-catalyzed silicone elastomer
(Supplementary Fig. 2). In total 20 vol% ethanol was chosen as
optimal composition.

We show the material as an artificial muscle that can be
electrically actuated using a thin resistive wire (Fig. 1a) and
low power characteristics (8 V, 1 A) to exhibit significant
expansion-contraction ability (Fig. 1b).

MethodsMaterials

We used platinum-catalyzed two-part silicone rubber Ecoflex 00-50
(Smooth-On, PA, USA) as a matrix material and ethanol ≥ 99.5%
(Sigma Aldrich, MO, USA) as an active phase change material.
Properties of the silicone rubber are shown in Table 1 below.
Material preparation involves thorough hand-mixing of 20 vol% of
ethanol with silicone elastomer (first with part A for about
2 min, then mixed with part B for about 2 min). The material is
ready-to-cast and ready-to-print after the preparation. Room
temperature curing of the cast or 3D-printed part takes up to 3 h.
A commercially available 0.25 mm diamter Ni-chrome resistive wire
was used for electrically driven heating of the artificial muscle
(i.e., for the actuation). To comply with the expansion of the
actuator material, a helical spiral shape was chosen for the Ni–Cr
wire. The wire was hand-wound on an 8 mm screw driver shaft as
shown in Supplementary Fig. 6.Figure 1

Soft artificial muscle. The muscle is composed of ethanol
distributed throughout the solid silicone elastomer matrix. a
Electrically actuated muscle including thin resistive wire in a
rest position on a human hand. b Expanded muscle actuated (8 V,
1 A)

Figure 2

Liquid ethanol evaporates with temperature, giving rise to
internal pressure inside the bubbles, which results in slightly
expanded silicone elastomer matrix. When ethanol passes the
liquid–vapor phase transition, extreme volume change occurs and
the silicone elastomer matrix significantly expands. With growth
in local pressure, the boiling temperature increases and thus,
continued heating to temperatures slightly higher than 78.4 °C is
required for further expansion, until no liquid ethanol remains in
the bubbles (Fig. 2b). Infrared radiation images of the material
at room temperature and during expansion (using Ni–Cr spiral) are
shown in Fig. 2d...

Mechanical properties

A maximal volume expansion of about 915% was measured at the
temperature of 90 °C during controlled heating in a wide water
bath (unconstrained volumetric expansion). We used an Instron
machine to measure the blocked directional force and actuation
stress characteristics of the material during its electrical
actuation using resistive spiral-shaped wire at low power (15 V, 1
A). ..

Implementation in robotics

We demonstrate the implementation of our composite material as an
actuator in a variety of robotic applications (Supplementary Movie
2). First, we show a McKibben-type muscle. Our self-sufficient
artificial muscle does not require any compressors or
pressure-regulating equipment (Fig. 4a), and is capable of lifting
weight much larger than its own (for example, a 13 g actuator
lifts 1 kg in Fig. 4b). We demonstrate its use as a bicep, which
contracts and pulls the lower arm up, causing it to bend at the
elbow (Fig. 4c). The actuator is comprised of the composite
material placed inside a braided mesh sleeving, fixed at the edges
(Supplementary Fig. 3). The actuation is electrically driven using
a spiral-shaped resistive wire (powered at 30 V, 1.5 A) passing
inside the actuator. During the actuation, the composite material
expands radially and contacts longitudinally, mimicking natural
muscle behavior...

Discussion

The proposed soft composite material demonstrates a combination of
high strain (up to > 900%) and correspondingly high stress (up
to 1.3 MPa) at low density (0.84 g cm−3). Even at 100% strain the
material develops stress of 0.4 MPa and is capable of lifting
weight about 1700 times greater than its own. These
characteristics place this material in previously inaccessible
region of the actuator stress–strain charts (Fig. 5a). Our
actuators are Pareto-undominated in specific actuation stress
versus strain (Fig. 5b). We suggest that the strain limit of our
material is the maximal strain of the silicone elastomer matrix
(980%, according to the manufacturer). Along with its extremely
low cost (laboratory cost of about 3 cent per gram), ease of
fabrication, and environmental friendliness, these properties make
this material an attractive solution where strain density is a
critical factor...

Figure 7

Agonist-antagonist soft actuator pair (20 V, 1 A). a Initial
position of biceps and triceps actuators; b Actuation (bending
the arm) by biceps; c De-actuation (bringing the arm to its
initial position) by triceps. Actuators size: 20 mm diameter,
100 mm length. This setup reduced actuation time by a factor of
2.4 compared with a single actuator

To summarize, our work proposed a self-contained soft robust
composite material, combining very high strain and reasonably high
stress with low density, which is easily produced from
bio-compatible components at a very low cost. This
material-actuator may serve in a variety of applications, from
traditional robotics to advanced bio-medical needs, and may enable
a new kind of entirely soft robots...

Hod Lipson is a roboticist who works in the areas of artificial
intelligence and digital manufacturing. He and his students love
designing and building robots that do what you’d least expect
robots to do: Self replicate, self-reflect, ask questions, and
even be creative...

Disclosed are devices, systems, apparatuses, methods, products,
and other implementations of vapor pressure solids. In some
embodiments, a vapor pressure solid may include a one- or
multi-component matrix material. In some embodiments, the
multi-components matrix material is a two-part PDMS comprising a
first and second matrix material. The first matrix material is
capable of being mixed with one or more vaporizable fluids that
causes the first matrix material to swell. The second matrix
material is capable of being mixed with the swelled first matrix
material to produce an actuating material. When the actuating
material is heated, the one or more vaporizable fluids expand,
resulting in vapors. The increased pressure applied by the vapors
causes the actuating material to expand.

BACKGROUND

Actuating or 'smart' materials address the increasing needs of
creating engineered material systems that provide diverse features
relating to mechanical actuation, sensor abilities and artificial
intelligence integration among others. Typically, these types of
actuating materials are biologically inspired materials that
integrate biological concepts and features in their structure and
microstructure in order to create controllable and adaptive
functionality of the material systems in which they are
integrated. Furthermore, actuating materials rely on converting an
input energy into a type of mechanical output such as force or
displacement. As a result, they require the use of a prime mover
(e.g., fluid, electromagnetic force etc.) and mechanisms to
convert the functions of the prime mover to the desired effect.
However, conventional actuating materials are inefficient. For
example, the use of fluids in actuating materials requires
hydraulic systems in order to provide adaptive control. Such
hydraulic systems require the use of electric motors to power them
and may also be prone to faults and defects. As a result, this may
require several components that are not easily manufactured and
that impair the ability to miniaturize the actuating system.
Further, these components are not easily created with 3D printing.

SUMMARY

In some embodiments, methods and articles of manufacture for vapor
pressure solids are provided. Specifically, articles of
manufacture for electrochemical actuating materials are provided
along with techniques for using and making the same. The methods
disclosed herein, allow for the creation of 'smart' materials that
can be controlled to provide adaptive functionality by applying
electrically controlled chemical reactions and/or chemomechanical
reactions that result in a change of volume (e.g., displacement)
and a conversion of input energy to mechanical energy. Actuating
materials are increasingly used in areas where conventional
actuators may not be suitable. Exemplary applications of such
actuating materials can be found in microscopic and nano devices,
robotic implementations (e.g., walkers, grippers, etc.),
medical/biomedical devices, sensors, chemical equipment and
architectural constructions.

[0005] In some embodiments, actuating materials are formed by
composite materials that include one or more materials that can
have different physical and chemical properties, and which when
combined, can produce characteristics that are different from the
properties of the individual components. Moreover, such actuating
composite materials further include sensing, actuation and
computation features. Such composite materials include at least
one constituent material identified as a matrix material. For
example, the matrix material surrounds and supports other
reinforcement materials that enhance the matrix properties. In
some embodiments, the actuation composite materials can include
matrix components such as silicone rubber, latex, polymers (e.g.,
Polydimethysiloxane ("PDMS"), platinum-catalyzed PDMS,
tin-catalyzed PDMS), resins etc. Accordingly, such materials do
not require mechanical or hydraulic components for actuation
purposes.

[0006] In some embodiments, the matrix material is infused by one
or more vaporizable fluids, which effectively creates a
combination of the matrix material properties and those of the
infused fluid into a single bulk material. For example, such
vaporizable fluids can include water, ethanol, acetone, glycerine,
etheric compounds and/or other suitable fluids. In some
embodiments, the fluid-infused composite materials are exposed to
heat, which initiates a phase transition process for the
vaporizable fluid (e.g., liquid-vapor transition). Specifically,
heating the fluid will produce vapors that can apply pressure and
inflate the matrix material due to a phase change (e.g.,
liquid-vapor) and/or due to a volume change, causing it to expand
and stretch based on its physical properties. In addition, the
heating of the vaporizable fluid can be achieved in a controlled
manner such that the resulting expanded material can simulate the
properties of biological tissue (e.g., muscle). In some
embodiments, heating can be accomplished using various techniques.
For example, heating can be accomplished by simple exposure of the
bulk material to ambient temperature gradients, submersion of the
bulk material in a water bath of increasing temperature,
application of hot air using a heat gun, embedding of thermal
elements (e.g., resistors) directly into the bulk material, mixing
of conductive material (e.g., black carbon) during the
manufacturing process of the bulk material and/or suitable
combinations thereof. In some embodiments, controlled heating can
be accomplished manually and/or automatically. Specifically,
controlled heating may be employed using control feedback systems
(e.g., proportional-integral-derivative ("PID") controllers,
autonomous learning using machine learning, etc.) that can be
external to or embedded within the actuating material measuring
both external and/or internal temperature gradients. In addition,
controlled heating can be performed in a uniform and/or
non-uniform manner for one or more actuating materials, thus
allowing for the actuation of complex structures. Such an
actuation material can be used in biomimetic robotic
implementations and/or as a sensor device. In some embodiments,
the heating of the composite material can be performed in selected
areas and/or on independent portions of the material. Furthermore,
condensing the vapor by, for example, reducing the heating (or
e.g., cooling) of the material can result in the contraction of
the matrix material to its original state. In some embodiments,
such functionality of the actuating material can be adaptively
controlled to operate as a sensor (e.g., pressure, temperature
sensor).

[0007] In some embodiments, the actuating material can also
include a seal to ensure that the vaporizable fluid is not able to
escape the matrix material. Moreover, additional mechanical
components can be used and/or embedded in the material (e.g.,
pistons, springs, heating elements) to increase the energy output
and/or force of the actuating material and allow for its use in
different systems such as valve piping equipment, chemical
equipment, etc. In some embodiments, reanimation of the actuating
material can be performed by injecting, using infiltration,
extraction and/or suitable procedures that reinfuses the matrix
material with the vaporizable fluid to recover and/or configure
the functionality of the matrix material.

[0008] In some embodiments, the actuating material can be used as
an actuator in soft robotic applications. Specifically, the
expansion and contraction of the actuating material can be used to
facilitate the motion or manipulation of other robotic components.
For example, a soft robot can include actuating material coupled
to a front leg and a rear leg. Actuation and contraction of the
actuating material will cause the front leg and/or rear leg to
move, advancing the soft robot in a direction along the axis of
contraction. In some embodiments, the soft robot can include a
gripper having two fingers for manipulating an object. Actuation
of the actuating material will cause the fingers to move inwards
in a grasping motion and lock onto an object.

BRIEF DESCRIPTIONS OF THE DRAWINGS [0009] FIG. 1 is an example of a process that provides an
actuating material in accordance with some embodiments of the
disclosed subject matter. [0010] FIG. 2 is an example of manufacturing an actuating
material in accordance with some embodiments of the disclosed
subject matter. [0011] FIG. 3 is an example of an actuating material in
accordance with some embodiments of the disclosed subject
matter. [0012] FIG. 4 is an example of a heating component for an
actuating material in accordance with some embodiments of the
disclosed subject matter. [0013] FIG. 5 is an example of an actuating material
including a heating component in accordance with some
embodiments of the disclosed subject matter. [0014] FIG. 6 is an illustration of an actuation of a
vapor pressure solid actuating material in accordance with some
embodiments of the disclosed subject matter. [0015] FIG. 7 is an illustration of preparing and
actuating a vapor pressure solid actuating material in
accordance with some embodiments of the disclosed subject
matter. [0016] FIG. 8 is an illustration of an actuation of a
vapor pressure solid actuating material in accordance with some
embodiments of the disclosed subject matter. [0017] FIG. 9 is a graphical representation of a
strain-stress curve for a vapor pressure solid actuating
material in accordance with some embodiments of the disclosed
subject matter. [0018] FIG. 10 is an example of an actuating
material shown during its initial phase (FIG. 10A) and its expanded phase (FIG. 10B) in accordance
with some embodiments of the disclosed subject matter. [0019] FIG. 11 is an example of a soft-robot using an
actuating material (FIG. 11C) illustrated during its initial
phase (FIGS. 11 A, 1 1D), its expanded phase (FIGS. 1 IB, 1 IE), in accordance with some embodiments of the
disclosed subject matter. [0020] FIG. 12 is an example of a soft-robot using an
actuating material in accordance with some embodiments of the
disclosed subject matter.

DETAILED DESCRIPTION
[0021] The disclosed subject matter relates to vapor pressure
solid articles and methods for making and using the same. In some
embodiments, vapor pressure solids refer to actuating (e.g.,
'smart') materials that are capable of producing an output force
and/or displacement as a result of a chemical reaction. For
example, such materials include matrix materials that are infused
with a vaporizable fluid that can expand and/or contract the
matrix based on its temperature. Additionally, these types of
materials do not require additional mechanical components to
provide the actuation (e.g., hydraulics, motors etc.) and, as a
result, they can be manufactured in bulk using smart geometric
design (e.g., 3D printing) and allow for miniaturization, thus
enabling uses in various bio-inspired applications.

[0022] In the following description, reference is made to the
accompanying drawings that form a part hereof, and in which are
shown by way of illustration specific embodiments in which the
inventive principles may be practiced. It is to be understood that
other embodiments may be utilized and structural changes may be
made without departing from the scope of the disclosed subject
matter.

[0023] FIG. 1 illustrates an exemplary method 100 for actuating a
vapor pressure solid material in accordance with embodiments of
the disclosed subject matter. Initially, at 102, a composite
material including at least one constituent material (e.g., a
matrix material) is provided. Specifically, a matrix material is
selected to provide support to other materials and can include
matrix components such as silicone rubber, latex, polymers (e.g.,
PDMS, platinum-catalyzed PDMS, tin- catalyzed PDMS), resins, or
other suitable materials. In some embodiments, such a composite
material can be constructed using a 3D printing technique or other
suitable composition procedures. Matrix materials and vaporizable
fluids can be chosen based on their chemical compatibility with
each other, and other respective properties, such as the fluid's
boiling point and handling restrictions, the matrix material's
mechanical properties, or suitable properties.

[0024] At 104, the matrix material can be infused with a
vaporizable fluid. In some embodiments an infusion can be
performed using injections, infiltration of the matrix material or
by using mechanical apparatuses (e.g., a Soxhlet extractor) or
using suitable combinations thereof. In some embodiments, an
infusion can consist of combining the vaporizable fluid with the
matrix material, captivating the vaporizable fluid and/or soaking
the matrix material in the vaporizable fluid. Additionally, in
some embodiments the vaporizable fluid can include water, ethanol,
acetone, glycerine, etheric compounds and/or other suitable
fluids. Moreover, in some embodiments, a combination and/or
emulsion of fluids can be automatically selected based on
thermodynamic properties and desired output force from the
actuating material. In some embodiments, the matrix material can
be infused in an adaptive manner and at different concentrations
so as to create the desired output.

[0025] At 106, the matrix material is sealed to create an
insulation for the vaporizable fluid. In some embodiments, a
sealing layer can be included in the matrix material using
suitable materials or combinations thereof. Additionally, in some
embodiments, the sealing layer can be a conductive material.

[0026] At 108, the matrix material, sealing layer and vaporizable
fluid are heated so as to cause the fluid to vaporize. In some
embodiments, heating can be accomplished using a heating element
(e.g., one or more resistors embedded in the material) or through
conductive heating by applying an adaptively controlled electrical
current through the actuating material. For example, in such cases
the actuating material can be modified to include one or more
conductive elements and can be used alone and/or in combination
with a conductive heater. Additionally, in some embodiments, a
heating exchanger can be used to control the heating and/or
cooling rates of the vaporizable fluid and subsequent expansion
and contraction rates of the actuating material. Faster heating
can be achieved using higher current or additional distributed
heating networks, resulting in quicker vaporization of the
vaporizable fluid. Similarly, faster cooling rates can be achieved
based on the actuator's form-factor, surface-to-volume ratio, and
convection currents. [0027] At 110, heating of the vaporizable
fluid results in the vaporization of the fluid, and the solid is
inflated based on the pressure of the vapor. Specifically, such
inflation of the bulk solid can be a result of the phase
transition (e.g., liquid- vapor) and/or continuous expansion of
the vapors. As a result, the actuating material can be dynamically
stretched and/or contracted based on the vapor pressure infused in
the matrix material. Moreover, the phase transition of the
vaporizable fluid into vapor combined with the one or more matrix
materials can cause large expansion of the matrix, which is not
typically obtained through other actuating methods. In some
embodiments, the actuating material can be used in a bimorph
configuration to allow for mechanical structures that are
independently controlled and can produce composite output forces.
For example, such composite materials can be included in piston
enclosures to provide pneumatic functionality. Additionally, the
actuating material can also include mechanical components (e.g.,
springs) in order to increase the output force and/or
displacement.

[0028] FIG. 2 shows an example of mixing process 200 of the
composite material with the vaporizable fluid as discussed in
connection with FIG. 1 (e.g., element 104). For example, in some
embodiments, a first part of PDMS gel (PDMS Part-A) composite
material 202 is mixed with various amounts of ethanol (0-33vol%)
204. As a result, the mixed ethanol causes swelling of the PDMS
Part-A gel as shown at 206. Subsequently, at 208, a second part of
PDMS gel (PDMS Part-B) is added to the swelled gel and mixed
thoroughly in order to obtain the bulk actuating material at 210.
Specifically, such mixing process, allows for the introduction of
air bubbles, occupied by the vaporizable fluid, in the cured
actuating material providing a solid that contains isolated pores,
which can be inflated upon the phase transition (e.g.,
liquid-vapor) and/or continuous expansion of the vaporizable fluid
(e.g., ethanol). In some embodiments, the vaporizable fluid
spreads in the inner walls of the bubbles while air and vapors
remain in the inner part of the bubbles and causes expansion upon
heating. In some embodiments, the mixed material is both castable
and 3D-printable, and will solidfy in room-temperature curing.
During the curing, the vaporizable fluid occupies the air bubbles,
and creates new pores. The pores are expanded until equilibrium
between the internal vapor pressure and external environment
pressure is achieved. In some embodiments, the density of the
mixed material including 20 vol.% ethanol is 0.84g/cm<3>.

FIG. 3 shows an example 300 of a vapor pressure solid actuating
material in accordance with some embodiments of the disclosed
subject matter. Specifically, vapor pressure solid 302 includes a
PDMS elastometric matrix material as described in connection with
FIG. 1 that is infused by a low-melting liquid such as ethanol.
Specifically, the fluid is infused in the matrix material by
mixing until the material exhibits swelling properties and the
ethanol liquid is fully integrated with the PDMS matrix material.
For example, in some embodiments, desired properties of the
actuating material can be achieved by adding 0.5ml of liquid to
each 1ml of PDMS. Upon mixing, the material is left for curing to
ensure full integration of the vaporizable fluid in the matrix
material. In some embodiments, curing times can be adaptively
controlled to allow for different properties of the resulting
actuating material. After curing, a soft solid material with
entrapped fluid is obtained (e.g., 302). The actuating material is
capable of significantly expanding upon heating (e.g., 100vol. %)
and contracting to its initial dimensions upon cooling.

[0030] FIG. 4 shows an example 400 of a conductive heater that can
be embedded in the actuating material in accordance with some
embodiments of the disclosed subject matter. Specifically,
conductive heater 402 can be produced using 3D printing techniques
wherein the composite materials include carbon black and PDMS
matrix material infused in ethanol or other suitable fluids. For
example, in some embodiments, carbon black material can be added
to the PDMS along with ethanol by a ratio of O. lg carbon black
and 0.5ml ethanol to each 1ml of PDMS. The materials can be mixed
and left to cure in order to provide the desired electrochemical
properties. For example, such a conductive heater can exhibit a
resistance of less than 100 Ohm, capable of conducting electrical
current and allowing for rapid Joule heating while cooling down
rapidly when the heating is terminated.

[0031] FIG. 5 shows an example 500 of a vapor pressure solid
actuating material deposited inside the conductive heater 502 as
described in connection with FIG. 4. Deposition of the vapor
pressure solid can be performed in various suitable manners. In
some embodiments, contact between the conductive heater and the
vapor pressure solid can result in adaptively controlling the
actuation of the material using selective alteration of heating
and cooling cycles by means of allowing and/or interrupting the
passing of the electrical current through the conductive heater.
Higher current or more evenly distributed heating can produce
faster expansion. Similarly, better thermal conductivity can
produce faster cooling.

[0032] FIG. 6 shows an example 600 of the different phases of an
actuating material

(e.g., vapor pressure solid) during heating as described in
connection with FIG. 1. Specifically, matrix material 602 (e.g.,
silicon rubber matrix) is infused by vaporizable fluid 604 (e.g.,
ethanol) by for example soaking and curing while at room
temperature. Subsequently, upon heating the composite material 602
using a heating element and/or a conductive heating technique,
vaporizable fluid 604 commences to produce vapors 606. As a
result, composite material 602 begins to expand and actuates a
force and/or displacement of volume based on the pressure of the
vapor.

[0033] FIG. 7 shows an example 700 of the different microscale
phases of the preparation and actuation of the bulk actuating
material (e.g., vapor pressure solid) as discussed above in
connection with FIGS. 2 and 6. Specifically, at 702, swelled PDMS
gel infused with ethanol 210 is casted and molded in order to cure
and attain its final physical properties (e.g., harden, bond etc.)
In some embodiments, molding and shaping can be performed
automatically using 3D printing. At 704, the actuating material is
at the early stages of curing whereby the infused vaporizable
fluid (e.g., ethanol) has not yet reached its boiling temperature
(e.g., 78.4 °C). Subsequently, as the actuating material is
introduced to increasing temperatures at 704 the ethanol liquid is
exposed to a rising vapor pressure, which leads to an initial
volume expansion of the actuating bulk material as it approaches
the fluid's phase transition boiling point (e.g., 78.4 °C) at 706.
In some embodiments, such initial volume expansion can reach up to
50% of the original volume. Importantly, once the temperature
reaches the fluid's phase transition point (e.g., boiling point)
at 708, the vaporizable fluid (e.g., ethanol) will commence to
boil leading to an immediate increase of the pressure within the
bulk material. As a result, at 710, the actuating material will
start to expand due to the gas expansion in order to equalize the
external and internal pressure. In some embodiments, such volume
expansion can reach up to 900% of the original volume at a
temperature of 95 °C.

FIG. 8 shows an example 800 of the different actuation phases of
the bulk actuating material (e.g., vapor pressure solid) and the
relationships between the local volume, boiling temperature and
local pressure. For example, at 802 while the actuating material
is at rest (e.g., room temperature, pressure) no volume expansion
is observed. At 804, as the material is exposed to increasing
temperatures reaching the boiling point of the vaporizable fluid,
the local pressure of the material increases. As a result, the
volume of the material exhibits an initial expansion, while the
boiling point of the fluid also increases requiring the exposure
of the material to constantly increasing temperatures in order to
sustain the actuation. At 806, once the temperature has exceeded
the boiling point of the vaporizable fluid, the volume expansion
is maximized as is the local pressure. In some embodiments, such
volume maximization allows for the actuating material to lift
weight that is 6000 times that of its own. [0035] FIG 9 shows a
graphical representation of results obtained for the disclosed
vapor pressure solid actuating material compared to other
actuating materials. Graphic 900 represents a stress-strain curve
of the different materials whereby stress refers to an internal
force within the material associated with the deformation of the
material and strain refers to the relative change in shape and
size (e.g., deformation) of the material. Graphic 900 shows that
the vapor pressure solid actuating material exhibits the highest
strain (e.g., deformation) while experiencing moderate stress to
achieve the illustrated strain. As a result, such actuating
material, which does not require the use of additional equipment
to induce actuation can be used for low-cost, safe and
controllable miniature soft actuation systems.

[0036] FIG. 10 shows an example of a vapor pressure solid
actuating material 302 as discussed previously in reference to
FIG. 3. Specifically, actuating material 302 is depicted before
(see FIG. 10A) and after (see FIG. 10B) the phase transition
process (e.g., liquid-gas transition) of the vaporizable fluid
(e.g., ethanol) that results to the expansion of the vapor
pressure solid due to increased heating. The vapor pressure solid
can be electrically-actuated with a thin-resistive wire operated
at low power characteristics (e.g., 8V and 1 A).

FIGS. 11A-11E) in accordance with some embodiments of the
disclosed subject matter. In some embodiments, actuating material
302 is formed onto a layer of passive PDMS material 1104 and is
used with rigid component 1102 that is able to move as a result of
the expansion of the vapor pressure solid actuating material (see
FIGS. 11A -11B). The passive PDMS material 1104 is formed with a
first end 1108 and a second end 1110. In some embodiments, the
first end 1108 is formed with solid materials, and the second end
is coupled to the rigid component 1102. A notch 1106 can be formed
in the actuating material 302 to facilitate bending. During
actuation, the actuating material 302 expands and pushes the first
end 1108 inwards along the axis of contraction. The actuation
motion causes the first end 1108 to push against the floor and
causes the rigid component 1102 to move in the opposite direction,
along the axis of contraction.

[0038] In some embodiments, the layer of passive PDMS material
1104 includes a solid first end 1112 and a soft second end 1114
(see FIG 11C). During actuation, the actuating material 302
expands and bends due to the constricting force near the vicinity
of the passive PDMS material 1104. As the actuating material 302
bends, the soft second end 1114 is pulled inward advancing it
along the axis of actuation. During contraction of the material,
the solid first end 1112 advances along the same axis while the
soft second end 1114 remains in place, causing the soft-robot to
move.

[0039] In some embodiments, the layer of passive PDMS material
1104 includes a gripper having a first finger 1116 and a second
finger 1118 (see FIGS 1 1D and HE). During actuation, the
actuating material 302 expands and bends causing fingers 1116 and
1118 to move inwards in a grasping motion. The actuating material
302 can remain actuated allowing the fingers 1116 and 1118 to
grasp and lock onto an object. The force applied by fingers 1116
and 1118 can be adaptively controlled to enable further
manipulation of the object. The fingers 1116 and 1118 can be
coupled to a moveable robotic arm 1120 enabling further
manipulation and movement of the object. The fingers 1116 and 1118
can be constructed of soft materials ensuring the safe
manipulation of fragile items, such as for example, an egg.

[0040] FIG. 12 shows a soft-robot using a vapor pressure solid
actuating material in accordance with some embodiments of the
disclosed subject matter. Specifically the actuating material is
enclosed in movable member 1202 and coupled to a resistive wire
conveying electrical current. The movable member 1202 operates
similarly to a piston and moves triangular base 1204 of a
pyramidal structure upon heating and subsequent expansion of the
enclosed actuating material. For example, when the actuating
material is actuated, the movable member 1202 moves an upper part
of bar 1206 in a forward direction. Upon contraction of the
actuating material, the bar 1206 exerts a force against the floor
moving the pyramidal structure in the forward direction. The
actuating material can move the pyramidal structure by applying
current (8V and 1A) through the resistive wire. In some
embodiments, the actuating material can be embedded in a Teflon
sleeve.

[0041] The embodiments described in this disclosure can be
combined in various ways.

Any aspect or feature that is described for one embodiment can be
incorporated into any other embodiment mentioned in this
disclosure. Accordingly, while various novel features of the
inventive principles have been shown, described and pointed out as
applied to particular embodiments thereof, it should be understood
that various omissions and substitutions and changes in the form
and details of the systems and methods described and illustrated,
may be made by those skilled in the art without departing from the
spirit of the invention. Amongst other things, the steps of any
described methods may be carried out in different orders in many
cases where such may be appropriate. Those skilled in the art will
recognize, based on the above disclosure and an understanding
therefrom of the teachings of the inventive principles, that
different configurations and devices can be used to implement the
general functionality and different embodiments of the inventive
principles. Any particular method components are for illustrative
purposes to facilitate a full and complete understanding and
appreciation of the various aspects and functionality of
particular embodiments of the present principles. Those skilled in
the art will appreciate that the inventive principles can be
practiced in other than the described embodiments, which are
presented for purposes of illustration and not limitation.

US2017042034SYSTEM AND METHODS FOR ADDITIVE MANUFACTURING OF
ELECTROMECHANICAL ASSEMBLIES

A hybrid additive manufacturing approach that incorporates
three-dimensional (3D) printing and placement of modules selected
from a library of modules to fabricate an electromechanical
assembly. By virtue of fabrication of the electromechanical
assembly, mechanical properties and electrical properties of the
assembly are created.

FIELD OF THE INVENTION

[0003] The invention relates generally to additive manufacturing.
More specifically, the invention is directed to a hybrid approach
that incorporates three-dimensional (3D) printing and placement of
modules selected from a library of modules to fabricate an
electromechanical assembly. By virtue of fabrication of the
electromechanical assembly, mechanical properties and electrical
properties of the assembly are created.

BACKGROUND OF THE INVENTION

[0004] Additive manufacturing is increasingly becoming a
significant fabrication technique, both in research and industrial
settings, applicable to a broad range of applications. Some
commercially important additive manufacturing examples include,
for example, low-cost rapid tooling manufacturing, low-volume
prototype and production runs, medium-volume automotive and
aerospace applications, dental restoration, orthopedic implants,
custom orthotics, and user-specific artificial limbs. Furthermore,
additive manufacturing methods have been used in biomedical
research settings to create heterogeneous tissues from individual
precursor cell types and to create functional replacements for
missing or damaged body parts.

[0005] Despite a great deal of effort and the diversity of
additive manufacturing techniques, no additive manufacturing
process can fabricate high quality electrical interconnections,
computational circuits, sensors or actuators in combination with
mechanical elements in an integrated component, i.e.,
electromechanical component.

[0006] With Direct-Write electronics (“DW”), or the similar Direct
Print (“DP”) technique, it has been demonstrated that inkjet
printers are capable of fabricating transistors, and have used a
combination of inkjet or digital printing and Fused Deposition
Modeling (“FDM”) or Stereolithography (“SLA”) to create electrical
circuits within a 3D printed part. One interesting alternative
approach uses conventional semiconductor fabrication to create
very small semiconductor devices that are subsequently blended
with an ink binder. Although electromagnetic actuators fabricated
in one process via FDM and DP has been recently demonstrated, it
is rudimentary at best.

[0007] Despite this progress, enormous challenges must be
overcome. Synthesizing electrically conductive materials with
volume resistivity similar to bulk metals that can be extruded or
deposited in a low-temperature environment (so that is it
process-compatible with other materials in the assembly) remains
an elusive challenge. The current state of the art, available from
various vendors, employs powdered metal inks that are
solvent-borne and achieve volume resistivity that is four times
(4×) to ten times (10×) larger than bulk metal in the case of
silver, and 10× to 50× for copper. These materials require a
post-process sintering step, typically by heating to between 80
and 150 degrees Celsius (° C.) in order to achieve the stated
resistivity, which can be difficult to integrate with other
heat-sensitive components within the assembly. The active devices
such as transistors that have been fabricated thus far have lower
carrier mobility and lower on-off ratios than similar devices
fabricated in silicon.

[0009] In certain situations carrier mobility impacts the drain
current and the transconductance in a field effect transistor.
Larger drain currents are desirable for some applications;
however, as a consequence of lower mobility and larger oxide
thickness, printed organic transistors typically offer drain
currents that are several orders of magnitude smaller than
conventional devices. It has been found that wider channels can be
used to increase drain current, though this is usually accompanied
by increased leakage. Resolution limitations of current printable
electronics techniques impose a feature-size penalty of nearly
three orders of magnitude, relative to conventional semiconductor
fabrication techniques, which limits the amount by which the
channel length can be reduced.

[0010] Larger transistor feature sizes lead to increased parasitic
capacitances at each transistor, reducing their switching speed.
Lower transconductance also limits switching speed; the
propagation delay of recent fast organic transistors is at least
three orders of magnitude slower than conventional transistors,
limiting their use to relatively simple logic circuits since this
delay accumulates with each cascaded logic cell. Printed organic
semiconductors sacrifice endurance relative to conventionally
fabricated circuits, with published shelf- and operating lifetimes
ranging from several weeks to two years.

[0011] Conductor quality in printed electronics is impaired by
incompatible material processing requirements. Low-resistivity
base materials and narrow traces with high current-carrying
capacity are desired In order to achieve favorable conductivity,
electrically conductive materials are used. Electrically
conductive materials including conductive materials that can be
inkjet-printed or extruded are referred to as “inks”. These inks
typically require a post-print curing or sintering step that
entails heat-treating at temperatures ranging from 125 to 500° C.
for an extended period of time. Since this range exceeds the
glass-transition temperature of most common polymers used in
additive manufacturing, the sintering step can cause other
materials in the part to melt or degrade.

[0012] To circumvent this problem, alternative sintering
techniques have been developed based on chemical reactions,
resistive heating, plasma, photonic energy, and radio-frequency
heating. Recent results compatible with low-temperature polymer
substrates demonstrate conductor resistivity of 2-10× bulk via
pulsed Xenon lamps, and pulsed-laser, though integration of these
methods with structural additive manufacturing materials has not
been demonstrated. Reactive silver inks have been shown to yield
traces with conductivity nearly equal to bulk silver after 15
minutes of sintering at 90° C., though material costs may limit
this approach.

[0013] A commercially available method for creating electrical
conductors on the surface of plastic parts, known as Laser Direct
Structuring (“LDS”), uses a laser to ablate the thermoplastic
substrate where conductive traces are desired; organic-metallic
additives in the plastic are activated during this process,
leaving behind a surface that can be plated during successive wet
metallization steps. However, like the other methods mentioned
above, LDS creates electrical traces only on the surface of a part
and limitations in achievable trace thickness impose constraints
on current-carrying capacity despite continuing improvements in
material resistivity.

[0014] An alternative fabrication approach, Shape Deposition
Manufacturing (“SDM”), circumvents material and process
compatibility issues by embedding prefabricated components into an
assembly as it is being fabricated. This concept has been
demonstrated by embedding complete assembled circuit boards as
well as discrete components; these components are interconnected
with embedded wires or printed conductors subject to the
limitations discussed above. At a smaller scale, individual pieces
of prefabricated semiconducting material referred to as
“chiplets”, have been self-assembled to form functional arrays of
devices over large scales, including roll-roll manufactured LED
sheets, and flexible arrays of chip-scale solar cells. When
fabricated with high-speed electrical interconnects on their
edges, individual chiplets can be interconnected to form larger
composite circuit “Quilts”. A related approach also decomposes the
problem into separate high-temperature fabrication steps using
conventional micro-fabrication tools, followed by a
low-temperature assembly process based on transfer printing.

[0015] Existing manufacturing methods exist that embed components;
however these methods rely on special-purpose embedding of
particular components for specific designs. For example, U.S. Pat.
No. 5,278,442 to Prinz et al. discloses electronic components
formed in place by incremental material build-up of thin layers.
At least one mask is used per layer to form electronic components
made of conductors such as gold and copper, insulators such as
ceramic materials and possibly semiconductors, all of which are
applied by thermal deposition spray using a thermal deposition
spray.

[0016] Another example of an existing manufacturing method that
embeds components is described in U.S. Pat. No. 5,301,415 to Prinz
et al., which forms three-dimensional objects by applying segments
of complementary material and deposition material so as to form
layers of material. Selected segments of material are then shaped
after one or more segment is formed. In this manner, layers of
material form a block containing the object made of deposition
material and surrounded by complementary material, which may
subsequently be removed.

[0017] As further described in U.S. Pat. No. 5,286,573 to Prinz et
al., the support structure has a melting point lower than the
melting point of the deposition material so that the support
structure can be removed by a melting process.

[0018] With all of the above described methods, embedded
components are printed or shaped within a complementary material,
which may ultimately be removed. These components are specific to
the desired application of the assembly. Though multiple additive
material deposition techniques have been developed to address
diverse users, existing techniques fail to address three critical
requirements that electromechanical printers must satisfy. First,
existing methods produce components with electrical performance
that is inferior to conventionally produced electrical components
by several orders of magnitude. Second, existing methods are
incapable of combining the diverse materials required for complex,
integrated electromechanical systems. Thus, there is a need for
general-purpose, scalable manufacturing methods that employ a
library of pre-fabricated modular components that are universal in
manufacturing a variety of assemblies. Third, existing techniques
that embed components do not contemplate or demonstrate a modular,
general-purpose system. Instead they embed specific pre-fabricated
components that are unique to each intended end-use or
printed/assembled design. This limitation makes existing methods
incapable of addressing the need for a general-purpose
electromechanical 3D printer. The invention satisfies these needs.

SUMMARY OF THE INVENTION

[0019] The invention overcomes the material and process
limitations of current printable electronics approaches, enabling
complete, complex electromechanical assemblies to be fabricated.

[0020] The few available tools that integrate electrical and
mechanical design into an electromechanical design environment do
so by relying on the printed circuit board as a natural interface
between the electrical and mechanical functions of the assembly.
In making this choice, the traditional separations between
electrical and mechanical design are entrenched: the circuit board
has no mechanical functionality apart from the space that it
occupies, and the mechanical components merely provide a physical
substrate for the electronics. High-performance 3D-printable
electrical components cannot be fabricated by existing additive
manufacturing tools.

[0021] The invention is directed to finished parts with complex
electromechanical properties that can be simulated, designed and
fabricated. Specifically, the invention relates to an additive
manufacturing process that fabricates high quality electrical
interconnections, computational circuits, sensors or actuators in
combination with mechanical elements in an integrated
electromechanical assembly.

[0022] The invention is directed to a hybrid approach that
incorporates three-dimensional (3D) printing and placement of
modules selected from a library of modules to fabricate an
electromechanical assembly with mechanical and electrical
functionality comparable to conventionally produced planar printed
circuit boards. 3D printing processes includes a variety of
methods including, for example, Inkjet, Fused Deposition Modeling
(“FDM”), Stereolithography (“SLA”), Drop-On-Demand/Inkjet, or
Powder-bed/Binder-jetting, to name a few. Additive processes are
used in 3D printing in which successive regions of material are
laid down under computer control creating an object of any shape
or geometry, and may be produced from a 3D model or other
electronic data source. A component placement system is used to
position one or module components within the object during
printing.

[0023] According to one embodiment of the invention, module
components used in fabrication include both electrical
properties—also referred to as “electrical functionality”—and
mechanical properties—also referred to as “mechanical
functionality”—with each module component treated as an inherently
electromechanical object. This becomes increasingly true as the
module size decreases and the percent volume occupied by modules
within the assembly increases. Modules with unique physical
properties expand the variety available to designers.

[0024] The invention goes beyond previous system and methods that
employ either a single module type, or are not modular at all,
requiring components specific to the desired assembly design to be
loaded into a printer. In contrast, the invention relies on a
modular design philosophy: a small set of modules with generic
electrical and/or mechanical functionality can be combined, in
large numbers if required, to yield the desired performance.

[0025] Specifically, the invention incorporates different module
types—such as a microcontroller module, resistor module, capacitor
module, diode module, transistor module—that may be mechanically
similar, but have distinct electrical functionality, into a
3D-printed assembly as it is being fabricated. Each module may
include electrical functionality, mechanical functionality, or
both. In one embodiment, the invention employs continuous material
deposition via inkjet to create the portions of the assembly that
require mechanical functionality, and pick-and-place manipulators
to deposit modules wherever electromechanical functionality is
required.

[0026] The system and methods of the invention may be used to
fabricate any type of assembly, for example one that is activated
when a button is depressed on the surface of the assembly. The
system and methods of the invention may also be used to fabricate
assemblies that exploit the programmability provided by a
particular module.

[0027] Design tools such as 3D Computer Aided Design (“CAD”)
systems are used to create an assembly. The assembly is created to
incorporate modules by using volumes of space, or voids. A printer
creates regions from conventional inkjet material and modules are
positioned within the voids of the region portion created by the
printer. If necessary, heating is applied to fuse modules on
adjacent regions together or to fuse modules to the regions
themselves. This process continues until the assembly is complete.

[0028] According to the invention, the number of unique
combinations of module components positioned within a material is
endless. The combination and position of module components
determine the mechanical and electrical properties of the
electromechanical assembly.

[0029] In a specific embodiment, the invention incorporates a
limited repertoire of prefabricated modules with inkjet-deposited
photopolymers to create assemblies that incorporate complex
mixed-signal circuits with state of the art performance. This
modular technique is scalable, allowing a single machine to
produce finished parts with diverse functionality without being
reconfigured and immediately commercialized using available
technology.

[0030] One advantage of the invention, in contrast to related work
that embeds special-purpose circuit boards within a printed
assembly, the invention utilizes a small library of
general-purpose modules with atomic functionality. By controlling
the position and orientation of these parts within an assembly,
new electrical circuits can be fabricated without re-designing
individual circuit boards.

[0031] Electrical components are commercially available in
thousands of distinct physical packages. This heterogeneity, while
offering design flexibility, presents a challenge to methods that
directly embed commercially-available electronic packages, as it
requires package-specific descriptor libraries for each device
envelope and footprint to be developed.

[0032] Another advantage of the invention is that it reduces
designer workload by intentionally restricting the availability of
components to a predetermined set that have been fully specified,
facilitating circuit modeling via existing tools and eliminating
the need to develop new electrical package descriptions.

[0033] Component heterogeneity also presents challenges for
pick-place apparatus. Though conventional automated placement
tools are flexible enough to accommodate a variety of component
packages, these tools must be manually configured before each
production run, with operators loading in the particular
collection of components that will be used for the design. This
overhead currently limits low-volume printed circuit board
assembly; most commercial assembly providers employ manual
assembly at very low production volumes to circumvent the setup
cost. Since single-unit or ultra-low-volume production runs are a
key motivation for using additive manufacturing, setup costs must
be minimized, which argues for restricting the allowable
components to a small set that can be permanently maintained
within the printer.

[0034] In one embodiment of the invention, the allowable module
components are restricted to a small set that can be permanently
maintained within the printer through a library of modules. The
library houses prefabricated modules with the same configuration
in terms of size and shape, but differ with respect to electrical
functionality and/or mechanical functionality. The modules in the
library can support a variety of electrical functionality, such as
currents to at least 1 Amp (A), several orders of magnitude larger
than known comparable printed-electronics methods, and leverage
decades of progress in semiconductor fabrication. Complementary
metal-oxide-semiconductor (CMOS) processing steps for integrated
circuits may be used to allow digital logic to be embedded within
each module.

[0035] Methods that interconnect embedded commercial components
with printed conductors are limited by conductivity (limited by
conductor geometry and material volume resistivity), and process
temperature, while those that employ printed semiconductors
sacrifice drain current, on/off ratio, and switching speed. In
contrast, electrical connectivity according to the invention is
achieved through direct connections between adjacent modules,
yielding composite conductors that are nearly identical to
conventional copper traces.

[0036] The invention and its attributes and advantages will be
further understood and appreciated with reference to the
accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The preferred embodiments of the invention will be
described in conjunction with the appended drawings provided to
illustrate and not to the limit the invention, where like
designations denote like elements, and in which:

[0038] FIG. 1 illustrates a block diagram of an exemplary
system for fabricating an electromechanical assembly according
to the invention.[0039] FIG. 2 illustrates a perspective view of a module
component according to the invention.[0040] FIG. 3 illustrates schematic diagrams of select
module components according to the invention.[0041] FIG. 4 illustrates a flow chart of an exemplary
method for fabricating an electromechanical assembly according
to the invention.[0042] FIG. 5 illustrates a graphic representation for
fabricating an electromechanical assembly according to the
invention.

DETAILED DESCRIPTION

[0043] The invention demonstrates a capability that is impossible
with contemporary electronics printing methods, and would require
a costly electrical and mechanical design cycle, along with
special-purpose tooling if it were produced following conventional
electromechanical fabrication practice.

[0044] The invention is directed to a hybrid approach that
incorporates three-dimensional (3D) printing and placement of
modules selected from a library of modules to fabricate an
electromechanical assembly with both mechanical functionality and
electrical functionality comparable to conventionally produced
planar printed circuit boards.

[0045] FIG. 1 illustrates a block diagram of an exemplary system
100 for fabricating an electromechanical assembly according to the
invention. The system 100 facilitates a hybrid approach that
incorporates devices such as a printing apparatus 120 and a
component placement apparatus 140 to fabricate an
electromechanical assembly 200. The printing apparatus 120 may
include any type of printing functionality such as a 3D printing
machine. The component placement apparatus 140 may include any
type of selection and placement of components such as a high speed
pick-and-place machine including with parallel pick-and-place
techniques, or other similar techniques. Parallel fabrication
methods may be used to exploit the mechanical regularity of the
modules to manipulate entire regions simultaneously.

[0046] The printing apparatus 120 may access a material library
110 to obtain the material for printing. The material library 110
may include one or more different types of materials that may be
printed, for example, photopolymers or thermoplastics, although
any type of material may be used that is capable of being
deposited by a 3D printing machine, including for example an
inkjet process. The component placement apparatus 140 may access a
module library 130 for selection of module components for
positioning within the material printed by the printing apparatus
120. The module library may include different generic,
prefabricated module components that vary in electrical
functionality and/or mechanical functionality. Representative
module components are more fully described in reference to FIG. 2
and FIG. 3 below.

[0047] In certain embodiments, a fusion device 160 such as a laser
sintering machine may fuse the module components to one another in
order to form an electrical connection in order to realize
electrical properties. It is also contemplated the fusion device
160 may be used to fuse the module components to the material
printed by the printing apparatus 120.

[0048] In addition to the module components including mechanical
properties and/or electrical properties, the combination of
material printed from the printing apparatus 120 and module
components selected and placed by the component placement
apparatus 140 create the electromechanical assembly 200 with both
mechanical properties and electrical properties. Mechanical
properties include, for example, stiffness, strength, stress, and
strain. Electrical properties include any control of electrical
energy such as circuits including, for example, resistivity and
conductivity.

[0049] FIG. 2 illustrates a perspective view of a module component
200 according to the invention. Each module component 200
comprises a tile element 202 comprising a plurality of surfaces.
As illustrated, the tile element 202 is generally square in shape,
but any shape is contemplated. For example, the tile element may
be circular, spherical, or rectangular parallelepiped, to name a
few examples. In one specific embodiment, the tile element 202 is
a 3 millimeter (mm) square shape with a thickness of 0.9
millimeters (mm) in order to allow easy scaling to higher levels
of additive manufacturing. However, the invention is applicable to
module components of any size that are amenable to manipulation
using a component placement apparatus.

[0050] The tile element 202 includes one or more pads 205 that may
be used for connections. The pads 205 are shown on a top surface
of the module component 202, but pads may also be located on the
surface opposing the top surface. As an example, pad on the top
surface may be connected to pads on the bottom surface by a via in
each pad. It is also contemplated that the pads may provide
programming signals, enabling the printing apparatus 120 (FIG. 1)
to individually program each module.

[0051] An electrical element 204 and/or a mechanical element 206
may be either positioned on a surface of the tile element 202 or
within a surface of the tile element 202 in order to create
functionality/properties—electrical/mechanical—for the
prefabricated module component 200 for entry into the module
library 130 (FIG. 1). The surface opposing the surface that
includes the electrical element 204 and/or a mechanical element
206 is generally planar. Electrical elements 204 control
electrical energy and may include, for example, 2-way connect,
4-way connect, crossover connect, resistor, capacitor, inductor,
diode, transistor, switch, and microcontroller, as seen
schematically in FIG. 3. Mechanical elements 206 control
mechanical energy and may include any working or moveable
function, such as a gripper or robot effector.

[0053] The system and methods according to the invention were used
to fabricate a 2.5-D interconnection in which neighboring modules
on the same region rely on offset modules above or below for
electrical connections. Electrical circuits are formed by creating
chains of modules on 2 or more regions. This approach allows new
modules to be added to an assembly at any vacant location,
avoiding interference fits that would otherwise require
high-precision placement or large mating forces. This 2.5-D
interconnection strategy is one of several contemplated
topologies; other strategies compatible with this invention
include full 3D interconnections (in-plane connections between
modules).

[0054] It is contemplated that all modules may share the same
mechanical interface, for example 3 mm square, 0.9 mm thick, with
four square pads on the top and bottom. These dimensions are
incidental, as they are driven by the printed circuit board
fabrication methods employed to produce the modules. The invention
is equally applicable to smaller modules produced via
micro-fabrication, with the added capability of embedding the
electronic functionality within, rather than on top of, each
module.

[0055] With the exception of the blank module 210 of FIG. 3), the
topside pads of each module are connected to their corresponding
bottom side pads by a via in each pad. Eight of the module types
implement carrier boards for commercially available electronic
components, breaking out disparate package connections into a
common format. While some modules support electrical elements 204
(FIG. 2) positioned on or within their top side, certain modules
may not have components on or within their bottom side in order to
facilitate automated manipulation. In alternate embodiments, the
electrical elements 204 and/or mechanical elements 206 may be
positioned on or within one or more surfaces of the module
component 200.

[0056] In particular embodiments, the FET modules 228, 230 support
drain currents in excess of 3 A and can be used with signals as
fast as 10 Megahertz (MHz). The microcontroller module 232 employs
an Atmel ATtiny10 that contains 1 kB of code space, 32 bytes of
RAM, an analog to digital converter, internal oscillators, and
timer circuitry. This module's pads may also provide programming
signals, enabling the printer to individually program each
microcontroller module as it is placed.

[0057] FIG. 4 and FIG. 5 illustrate exemplary methods for
fabricating an electromechanical assembly according to the
invention. Specifically, FIG. 4 is a flow chart and FIG. 5 is a
graphic representation.

[0058] As shown in FIG. 4 at step 402, material is selected and
deposited into a plurality of stacked regions, each successive
region positioned on top of the previous region. At step 404,
module components are are selected from a library of modules. The
module components are positioned into the material at step 406. In
certain embodiments, the module components may be fused together
or fused to the material as shown in step 408. At step 410,
mechanical properties and electrical properties are created by
virtue of fabrication of the electromechanical assembly.

[0059] FIG. 5 illustrates a graphic representation for fabricating
an electromechanical assembly. As shown in FIG. 5, step “A” is
directed to a first device 120 depositing material 122, for
example using an inkjet process, into a plurality of stacked
regions 502a with each successive region positioned on top of the
previous region. The plurality of stacked regions 502a forms a
base region portion 510a including one or more void elements 520
as constructed by the material 122 such as a photopolymer
material.

[0060] As shown by step “B”, a second device 140 such as a high
speed pick-and-place machine, selects a module component 240 from
the library of module components and positions the module
component 240 in one of void elements 522, 524.

[0062] As shown by step “E”, the high speed pick-and-place machine
140 selects module component 244 and positions it in void element
526.

[0063] In certain embodiments, a fusion device 160 as shown in
step “F”, such as a laser sintering machine, applies heat in the
form of a laser beam 162 in order to fuse the module components
240, 242, 244 to one another. The laser sintering machine 160 may
also apply heat to fuse the module components 240, 242, 244 to a
region portion 510a, 510b.

[0064] As shown in step “G”, material is deposited into a third
plurality of stacked regions 502c with each successive region
positioned on top of the previous region. The plurality of stacked
regions 502c forms a second top region portion 502c that
encapsulates all of the module components 240, 242, 244 forming an
electromechanical assembly 550. By virtue of fabrication of the
electromechanical assembly 550, mechanical properties and
electrical properties of the assembly are created.

[0065] The system and methods of the invention may be used to
fabricate any type of assembly, for example an LED keychain light,
activated when a button is depressed on the surface. The system
and methods of the invention may be used to fabricate assemblies
that exploit the programmability provided by a microcontroller
module.

[0066] For example, a microcontroller module may be programmed to
create specific pulse-trains such as those that correspond to the
on and on-off pulses in a particular infra-red (IR) remote control
protocol. These pulses can be used to turn an IR LED on and off,
controlling a remote device. Another example includes the
play/pause, jog forward, jog backward, volume up and volume down
functions, creating a 5-channel IR remote control. Each of the
assemblies employ the inkjet-printed material as a supportive
structure, and the remote utilizes a flexible material around the
buttons that allows motion during button-press events.

[0067] Another example of an assembly incorporates a LED into a
structure that has full electromechanical functionality.
Inkjet-produced areas can incorporate components such as
rack-and-pinion connections, captive hinges, and springs. When one
component is activated, one or more other components may be
activated. For example, when a component on a gripper is
activated, the gripper arms open and an internal switch closes,
activating an illumination component.

[0068] While the disclosure is susceptible to various
modifications and alternative forms, specific exemplary
embodiments of the invention have been shown by way of example in
the drawings and have been described in detail. It should be
understood, however, that there is no intent to limit the
disclosure to the particular embodiments disclosed, but on the
contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the scope of the
disclosure as defined by the appended claims.

US9487387SYSTEM AND METHODS FOR ACTUATION USING ELECTRO-OSMOSIS

FIELD OF THE INVENTION

The invention relates generally to micro-fluidics and more
specifically to a system and methods for creating very low energy
micro-scale and macro-scale mechanical actuators through use of
one or more electro-osmotic pumps.

BACKGROUND OF THE INVENTION

Most conventional mechanical pumps have issues with reliability
due, in part, to the moving components. However, pumps that do not
require moving components such as electro-osmotic pumps (EOPs)
make them suitable for a variety of applications, including for
example “lab-on-a-chip” devices, diagnostic devices, micro total
analysis systems (μMTAS), drug delivery systems, and separation
and mixing processes, as well as micro-processor cooling systems,
to name a few.

Electro-osmosis is used to pump fluids that contain some quantity
of charged species, such as positive and negative ions. An
electric double layer is a structure that appears on the surface
of an object when it is exposed to a fluid. The object might be a
solid particle, a gas bubble, a liquid droplet, or a porous body.
The electric double layer refers to two parallel layers of charge
surrounding the object. The first layer comprises ions adsorbed
onto the object due to chemical interactions. The second layer is
composed of ions attracted to the surface charge. This second
layer is loosely associated with the object. It is made of free
ions that move in the fluid under the influence of electric
attraction.

Most solid surfaces acquire a surface electric charge when brought
into contact with a liquid. When an electric field is applied
across the liquid, the ions in the double-layer migrate in the
field, which results in viscous drag to create bulk fluid flow and
generation of a net pressure. This effect is referred to as
electro-osmosic pumping, or EOP pumping. Specifically, EOPs
provide fluid flow due to movement of an electric double layer
that forms at the solid-liquid interface. Not only do EOPs
eliminate moving components, but EOPs also move fluid using the
electric field. EOPs can move low conductivity fluids and have a
greater pressure and flow rate change when compared to
conventional pumps.

Thus, there is a need for low energy mechanical actuators that are
of a simple design and construction. The invention satisfies this
need.

SUMMARY OF THE INVENTION

The invention exploits a widely used device in micro-fluidics, the
electro-osmotic pump (EOP), to create very low energy micro-scale
and macro-scale mechanical actuators. The EOP uses electrical
fields to move naturally occurring charged particles (ions)
through a fluid medium. As the ions move in response to the
applied field, they drag the (non-charged) fluid along,
establishing bulk flow. When confined to a narrow chamber, a
pressure gradient can be established. The combination of pressure
gradient and bulk flow performs mechanical work, for example,
fluid flow control (i.e. actuators, valves), linear actuators
(e.g. for artificial muscles), micro-electro-mechanical system
(MEMS) devices (e.g. micro-pistons in bulk silicon), and
quasi-sealed actuators that expand and contract to realize both
linear and bending motion.

The invention relies on individual micro-scale actuators that can
be combined in any number including to produce a macro-scale
actuator structure with better power density, increased
reliability and lower production cost. With the use of
electro-osmotic pumps, the invention enables actuators to be
constructed in a variety of embodiments, including for example, a
sheet structure, a piston structure, and a cellular structure, to
name a few.

When compared to the small number of other efforts that have
applied electro-osmotic pumping to actuation, the invention
improves on these efforts in two key areas: (1) production of
linear strain that can be scaled down for micro-actuators and
scaled up for macro-actuators, and (2) mass-production using
commercially available processes that is also cost-effective.

When compared to other types of hydraulic actuation, the invention
yields high-force, high-strain linear and rotary actuators that
are cheap to produce, and are at least an order of magnitude more
efficient. These actuators are extremely valuable to the robotics
community, since power generation and storage is one of the key
limiting factors for the performance of mobile robots. However,
these actuators are general purpose and can be applied to any area
in which low cost and energy efficiency are priorities.

Certain embodiments of the invention are particularly suited to
cost-sensitive areas, since they are intended to be produced with
a very high-volume reel-to-reel production technique that reduces
the individual component cost. Certain other embodiments are
intended to be the actuation building block for a new paradigm of
modular micro-machines. One goal is to provide a small set of
micro-fabricated modular building blocks that form the basis for
larger, more complex machines. The key different building block
types include computation, power storage and transmission,
structure, and actuation. Large numbers of these standardized
building blocks may be prefabricated to establish the building
blocks in specific locations in order to build an actuator
assembly.

Certain other embodiments of the invention integrate a plurality
of electro-osmotic pumps within a flexible material in order to
provide an actuator with uniquely controllable states. For
example, certain portions of the actuator can be curled up or
curled down while maintaining a somewhat rigid state while other
portions of the actuator can be soft and pliable. Therefore,
actuators of this embodiment enable low or zero-power rigid
portions.

Certain other embodiments may be of a more complex structure by
incorporating an inherently three-dimensional (3D) mechanism so
that the electro-osmotic pumps can move fluid vertically.

Specifically, the invention constructs micro-actuators that
require very few moving parts, which is far more efficient than
other hydraulic actuators, vastly simplifies the actuator design
relative to other micro-actuators, offers large force output, and
can be readily scaled to create macro-scale actuators that are
composed of millions of individual actuators.

Some advantages of the invention include, for example, the
creation of high efficiency actuators with a very low energy
requirement, actuators of simple design with very few moving
parts, actuators that can exude a large force output, and
actuators that are readily scalable from micro-scale to
macro-scale actuators.

The present invention and its attributes and advantages may be
further understood and appreciated with reference to the detailed
description below of contemplated embodiments, taken in
conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWING

The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate an
implementation of the invention and, together with the
description, serve to explain the advantages and principles of the
invention:

FIG. 1 illustrates an exploded view of one embodiment of an
actuator in the form of a sheet structure according to the
invention.FIG. 2 illustrates the actuator of FIG. 1 in a relaxed
state according to the invention.FIG. 3 illustrates the actuator of FIG. 1 in a contracted
state according to the invention.FIG. 4 illustrates a cross-section of another embodiment of
an actuator in the form of a piston structure according to the
invention.FIG. 5 illustrates another embodiment of an actuator in the
form of a cellular structure according to the invention.FIG. 6 illustrates the actuator of FIG. 6 with a portion
actuated to bend slightly according to the invention.FIG. 7 illustrates the actuator of FIG. 6 with a portion
actuated to curl upward according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

All electro-osmotic pumps exploit the natural equilibrium-state
distribution of ions at a fluid/solid interface. This
distribution, known as the electrical double layer, results in a
net charge on the solid and an equal, but opposite, net charge in
the fluid near the surface of the solid. This charged fluid can be
moved when an externally applied electric field is applied.

For exemplary purposes, the invention is discussed with respect to
three embodiments: a sheet structure, a piston structure, and a
cellular structure. However, it should be noted that the invention
is not limited to these three embodiments, but that
electro-osmotic pumps can be used to construct actuators in a
variety of embodiments.

In one embodiment of the invention, the actuator is in the form of
a sheet structure as shown in FIG. 1 through FIG. 3. FIG. 1
illustrates an exploded view of one embodiment of an actuator in
the form of a sheet structure 100 according to the invention. The
sheet structure 100 comprises a plurality of sheets—three sheets
120, 150, 170 as shown in FIG. 1 through FIG. 3; however, any
number of sheets are contemplated. Each sheet 120, 150, 170 are
constructed from a flexible, inelastic material such as a polymer.

The first flexible sheet 120 includes a first top side 122 and a
first bottom side 124. The first top side 122 and the first bottom
side 124 are coated with a first conductive layer 130 and the
first flexible sheet 120 comprises a plurality of first chambers
128.

The second flexible sheet 150 includes a second top side 152 and a
second bottom side 154. The second top side 152 and the second
bottom side 154 are coated with a second conductive layer 160.
Like the first flexible sheet 120, the second flexible sheet 150
comprises a plurality of second chambers 158.

A third flexible sheet 170 includes a third top side 172 and a
third bottom side 174, wherein the third flexible sheet 170
comprises a plurality of third chambers 178 of a honey-comb
arrangement 179.

As shown in FIG. 2, the second top side 152 of the second flexible
sheet 150 is fused to the third bottom side 174 of the third
flexible sheet 170 at a plurality of regular intervals and the
first bottom side 124 of the first flexible sheet 120 is fused to
the third top side 172 of the third flexible sheet 170 at a
plurality of regular intervals to obtain an assembled flexible
sheet structure 200 including a plurality of assembled chambers
220.

Each of the sheets 120, 150, 170 as shown in FIG. 1 can be mass
produced as a rolled sheet. The assembled flexible sheet structure
200 is then formed using a reel to reel process that fuses the
sheets 120, 150, 170 together at specific locations using heat and
pressure in order to produce specific chambers 220.

The assembled flexible sheet structure 200 is positioned inside an
outer membrane 250 that includes a working fluid 252 to form an
actuator 260.

For purposes of this application, a working fluid is any gas or
liquid that actuates the actuator. Examples of working fluids
include for example, water, steam, pentane, toluene,
chlorofluorocarbons, hydro-chlorofluorocarbons, fluorocarbons,
propane, butane, isobutene, ammonia, sulfur dioxide, helium, etc.

As shown in FIG. 2 and FIG. 3, the assembled flexible sheet
structure 200 contracts and expands to form a linear actuator when
a voltage is applied to pump the working fluid 252 across the
assembled flexible sheet structure 200 and into the plurality of
assembled chambers 220.

More specifically, the conductive layer 130, 160 enables a charge
to be externally applied. When opposite charges are applied to the
assembled flexible sheet structure 200—specifically the conductive
layers 130, 160—the working fluid 252 is forced through the
assembled chambers 220 and swells the chambers 220 formed by the
third flexible sheet 170 as shown in FIG. 3.

In one embodiment, it is contemplated that the chambers 220 range
from 200 nanometers to several micrometers, depending on the
design goals and the working fluid 252. In addition, it is
contemplated that the chambers 220 may be approximately one
millimeter in each planar dimension with the entire assembled
flexible sheet structure 200 being several hundred micrometers
thick. Again, these dimensions are not fixed and can be easily
changed depending on the specific goals. In general however, a
typical sheet structure actuator can employ hundreds of thousands
to millions of individual chambers in a single sheet. For example,
using the approximate chamber dimensions previously provided, a
sheet structure actuator 10 centimeters long that employs a rolled
sheet of chambers that is 10 centimeters long before being rolled
would contain over 100,000 individual chambers.

FIG. 2 illustrates the actuator 260 in a relaxed state whereas
FIG. 3 illustrates the actuator 260 in a contracted state
according to the invention. As shown in FIG. 3, the swelling of
chambers 220 stretches the flexible, inelastic sheets 120, 150,
causing a contraction. This motion can be exploited to create low
cost, batch-fabricated linear actuators such as artificial
muscles.

In another embodiment of the invention, the actuator is in the
form of a piston structure as shown in FIG. 4. In the piston
structure embodiment, the electro-osmotic pumps perform two
distinct functions: (1) pumping and (2) sealing. The pumping
function moves fluid from one side of the piston to the other,
forcing the piston to move. The sealing function prevents fluid
from slipping past the piston (between the piston and the chamber
wall) without also forcing the piston to move.

The piston structure according to the invention employs widely
used micro-fabrication techniques to create micro-pistons in bulk
silicon. This design yields high actuator force with low actuation
power, and exploits the electro-osmotic pump to avoid complex
seals at the pump/fluid boundaries.

In this piston structure embodiment, the invention is intended to
be implemented in traditional microelectromechanical systems
(MEMS) setting using bulk silicon and various etch and plate
stages.

The piston structure actuator 400 comprises a piston 402
positioned within an enclosed chamber 404. Specifically, the
piston 402 includes a head 406 and a cylinder 408. The enclosed
chamber 404 includes a plurality of outside surfaces 410 and a
plurality of inside surfaces 411. The head 406 of the piston 402
includes a plurality of perforations 412.

The enclosed chamber 404 is filled with a working fluid 414,
wherein the enclosed chamber 404 includes an aperture 416 through
which the piston 402 is positioned within the enclosed chamber
404.

The piston structure actuator 400 includes one or more electrodes
430. In one embodiment, the one or more electrodes 430 are
positioned on either side of one or more perforations 412 of the
head 406. In another embodiment, the one or more electrodes 430
are positioned at two opposing outside surfaces 410 of the
enclosed chamber 404. In another embodiment, the one or more
electrodes 430 are positioned at the aperture 416 of the enclosed
chamber 404. It is further contemplated that one or more
conductors 432 can be used to connect the one or more electrodes
430 to an outside surface 410 of the enclosed chamber 404.

In the embodiment with one or more electrodes 430 positioned at
two opposing outside surfaces 410 of the enclosed chamber 404, a
weaker electric field for the same applied voltage is realized,
but this embodiment avoids the need for conductors 432 that
connect the electrodes 430 on the piston 402 to the outside
surface 410 of the chamber 404.

The one or more electrodes 430 are configured to be charged to
create an electric field in order to move the working fluid 414
and actuate the piston 402. Specifically, when the one or more
electrodes 430 are charged, the resulting electric field causes
the working fluid 414 to flow from one insides surface 411 to
another inside surface 411 of the enclosed chamber 404 causing the
piston 402 to move.

More specifically, the pumping and sealing functions are both
accomplished by the same electro-osmotic pump that uses the one or
more electrodes 430 on the piston 402 itself, and is formed by the
gap 440 between the cylinder 408 and an inside surface 411 of the
chamber 404. When the electrodes 430 are energized, the working
fluid 414 is forced to flow within the gap 440, causing a bulk
flow of the working fluid 414 from one side of the piston 402 to
the other. This approach avoids flexible seals which are difficult
to fabricate and cause friction losses or stiction—the static
friction that needs to be overcome to enable relative motion of
stationary objects in contact.

It is also contemplated that a second electro-osmotic pump may be
implemented, separate and apart from the piston structure actuator
400, that moves working fluid from one side of the piston to the
other via microfluidic channels that lead to either side of the
piston (these channels might lead to either end of the chamber,
for example). This version is more complicated, but allows greater
fluid pressures and flow rates.

FIG. 5 through FIG. 7 illustrate another embodiment of an actuator
in the form of a cellular structure 500 according to the
invention. In this embodiment, the invention uses an array of
identical chambers that are separated by individually addressable
permeable layers. Rather than pumping the working fluid from
outside the assembly as described in the embodiment of FIG. 1
through FIG. 3, it uses pumps that separate different cellular
chambers to move the working fluid between chambers. This motion
swells some chambers while shrinking others. Some of these
chambers employ inelastic inner struts which bias the
contraction/expansion due to fluid motion to cause non-isotropic
expansion or contraction. This approach can yield actuators that
are sealed, yet realize both linear and bending motion.

Similar to the first embodiment described in FIG. 1 through FIG.
3, the cellular structure 500 comprises a plurality of sheets 520,
550 that are constructed from a flexible, inelastic material such
as a polymer.

The first flexible sheet 520 includes a first top side 522 and a
first bottom side 524. The first top side 522 and the first bottom
side 524 are coated with a first conductive layer 530 and the
first flexible sheet 520 comprises a plurality of first chambers
528.

The second flexible sheet 550 includes a second top side 552 and a
second bottom side 554. The second top side 552 and the second
bottom side 554 are coated with a second conductive layer 560.
Like the first flexible sheet 520, the second flexible sheet 550
comprises a plurality of second chambers 558.

As shown in FIG. 5, the second top side 552 of the second flexible
sheet 550 is fused to the first bottom side 524 of the first
flexible sheet 520 at a plurality of regular intervals to obtain
an assembled flexible cellular structure 500 including a plurality
of assembled chambers 570.

A working fluid 575 is positioned inside the flexible cellular
structure 500 to create the mechanical actuator, wherein the
plurality of assembled chambers 570 are separated by individually
addressable permeable layers 530, 560 such that voltage applied to
one or more individually addressable permeable layers 530, 560
causes the working fluid 575 to flow from one assembled chamber
570 into an adjacent assembled chamber 570 such that select
assembled chambers 570 of the plurality are configured to contract
and expand. Furthermore, an inelastic inner strut 580 may be
positioned within each assembled chamber 570 to bias the
contraction and expansion of the chamber 570.

FIG. 6 illustrates the actuator of FIG. 6 with a portion actuated
to bend slightly according to the invention. Working fluid 575
from four of the chambers 571 has been pumped into the four
chambers 571 directly above them causing the chambers 571, 572 to
swell or contract causing the entire assembled cellular structure
500 to bend.

FIG. 7 illustrates the actuator of FIG. 6 with a portion actuated
to curl upward according to the invention. Working fluid 575
pumped from chamber 591 into the chamber 592, causing chamber 591
to contract and chamber 592 to swell, which causes the actuator in
the form of a cellular structure 500 to curl upward. Specifically,
the resulting tension draws the ends of the actuator together.

Similar to the other embodiments of the invention, the actuator in
the form of a cellular structure 500 can be built on a reel-reel
process. As shown two sheets are stacked; however, multiple sheets
may be stacked in order to create a many-layer stack-up.